No action needed on derailment pollution: EPA

More than 1,200 tonnes of copper concentrate and hundreds of tonnes of freight spilled into the Edith River when a freight train was derailed in flash flooding.

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The Northern Territory environment watchdog says no legal action will be taken over last year's train derailment at Edith River near Katherine.

More than 1,200 tonnes of copper concentrate and hundreds of tonnes of freight spilled into the river when a freight train was washed off the rails during flash flooding about 300 kilometres south of Darwin.

The rail line was closed for two months while repairs were carried out.

The NT Environment Centre is outraged that no one will be prosecuted for what it calls one of the largest pollution events in Territory history.

The Territory's Environment Protection Authority says tests have shown that no actual environmental harm was caused.

It says a small amount of copper concentrate remains in heavily vegetated areas, in some places up to 5mm thick.

But it says the risk to humans and the environment is low.

About 50 tonnes of freight is also still missing.

Territory Environment Minister Peter Chandler says while he has not read the EPA report, he supports its findings, and is pleased the companies involved will continue to check the area.

"It's their mess, they need to clean it up," he said.

"I would like to think that they are not going to walk away from this, and there is some ongoing monitoring," he said.

"So far, so good, again."

The area will be assessed again in the dry eason.

The company to which the spilled copper concentrate belonged, Oz Minerals, says it does not comment on regulator reports.